tW generation

Hi everyone, my question is the next one. I'm trying to generate p p > t~ W+ [QCD], add process p p > t W- [QCD]. There are no processes, so I need to import model sm-ckm. But then I cannot launch it, because it stays for hours doing nothing. I'm using 4F. The same problem with p p > t w b, this time with no model imported besides sm. How do I run these processes at NLO?

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Hi Mar,
the problem with tw production is that, in the 5FS, the real emission can have contributions like g g> t W b with intermediate on-shell top, which need to be subtracted.
You can find details here
arXiv:1607.05862
Unfortunately, the automation of the subtraction used in that paper is not yet complete, so I don't think there is an easy way out (unless you kill the diagrams with intermediate tops by hand).
Note that if you do this in the 4FS, then the same problems will appear at the born level.
Let me know if you need more help on this.
Best,

I've been reading that paper, it says that I should set to zero the top mass amplitudes (if I want to treat it with the DR1) in the files matrix_*.f, in the cases, as you said, where t is intermeadiate. Where exactly can I find that in the file? I haven't been able to find it so far, I'm sorry. This is one of the files

the troublesome real emission will be the b b~ initiated one and the gg one. These (do grep Process matrix*.f) are
matrix_5.f and matrix_6.f
If you look at the feynman diagrams (e.g. in the corresponding ps or jpeg files), you see that diagrams involving a resonant top are
diagram 2, for matrix_5
and diagrams 2,4,7 for matrix_6.f

In order to set them to zero, edit the .f file (take e.g. matrix_6.f), where you have the end of the helas calls
C Amplitude(s) for diagram number 8
CALL FFV1_0(W(1,7),W(1,9),W(1,1),GC_5,AMP(8))
JAMP(1)=-IMAG1*AMP(1)-IMAG1*AMP(2)+AMP(5)+AMP(6)+AMP(7)
JAMP(2)=+IMAG1*AMP(1)+IMAG1*AMP(2)+AMP(3)+AMP(4)+AMP(8)

You must set to zero the AMP() that you do not want (in this case 2,4,7 ) right before the JAMP lines.
So in this case you would have
C Amplitude(s) for diagram number 8
CALL FFV1_0(W(1,7),W(1,9),W(1,1),GC_5,AMP(8))
AMP(2) = dcmplx(0d0,0d0)
AMP(4) = dcmplx(0d0,0d0)
AMP(7) = dcmplx(0d0,0d0)
JAMP(1)=-IMAG1*AMP(1)-IMAG1*AMP(2)+AMP(5)+AMP(6)+AMP(7)
JAMP(2)=+IMAG1*AMP(1)+IMAG1*AMP(2)+AMP(3)+AMP(4)+AMP(8)

The other partonic subprocesses follow in total analogy, note that the number of the matrix_x.f corresponding to the gg and bb~ initiated real emission may change, and also the number of the diagrams to be set to zero (there will always be 3 diagrams for gg and 1 for bb~).

This should work, please check that you manage to reproduce some number in arXiv:1607.05862

Thank you! I see... just one last question, since I don't know what does dcmplx(0d0,0d0) mean, when I want to eliminate resonant tbar from the processes, is it the same line? Or does it change because it is t bar and not t?

dcmplx(0d0,0d0) means the complex zero number in fortran.
For removing the t~, follow the procedure I have outlined, keeping in mind that the number of the matrix_X.f to be modified and of the diagrams (AMP(Y)) to be set to zero may change.
Cheers,